Adjustable french curves for circular arcs



,Sept.'8, 1970 I D. HAEFELE 3,526,965

ADJUSTABLE FRENCH CURVES FOR CIRCULAR ARCS FiIed Dec. 11, 1967 INVENTOR DIETER HAEF'ELE.

BY Z

' ATTORNEY United States Patent Office us. (:1. 35-177 1 Claims ABSTRACT OF THE DISCLOSURE A substantially generally spiral shaped rigid guide rule with a guide groove of the same spiral shape therein. A flexible body assembly, comprised of a plurality of flexible lamellas movably guided on each other and mutually displaceable, connected on the rule by a flexible guide rail engaged in the guide groove and disposed to flex to assume the curvature of the guide groove and in turn bend the flexible body assembly to various circular arcs as the body assembly is moved longitudinally along the guide rule. A pointer on said guide rail registers with graduations on the rule giving an indication of the radii of the body assembly edges.

BACKGROUND OF THE INVENTION The French curve of the invention described hereinafter is intended to replace the necessarily many curves which are presently commercially available under the designation of railway rules. In such rules, each desired circular arc is obtained by the adjustment of the radius of the rule. The present curve instrument also is for use in lieu of the well-known clear plastic French curves and has the advantage thereover that one curve instrument according to the invention can provide a range of curves only attainable with a multitude of the clear plastic curves.

SUMMARY OF THE INVENTION The invention is directed to a guide rule provided with a graduation for the adjustable curve radii, with a guide groove generally in the shape of a spiral in the rule, the tangent angle T of the spiral guide groove being defined according to the following approximation formula:

A body consisting of a plurality of flexible lamellas guided on each other and mutually displaceable forms a substantially flat body portion having longitudinal drawing edges, which is movably connected by means of a guide rail with the guide groove of the guide rule. The curvature of the flexible guide rail which changes to conform identically with the groove of the guide rule, imparts bending action to the lamellas of the body member to adjust the edges thereof to circular arcs of desired radii as the body member is moved along the guide groove.

Furthermore, the French curve of the invention is directed to a generally spiral-shaped guide rule curve,

3,526,965 Patented-Sept. 8, 1970 consisting preferably of three parts and in order to reduce the guide rule to a handy longitudinal length, according to the requirements of the invention, two parts are fitted together for longitudinal shifting movement along the rule. An interchangeable graduation scale is embedded in the rule which shows the adjusted outer and inner radius of the shifting part, which is flexible, in order to be able to provide a reading of the radii of the edges of the shiftable flexible part, in the diflierent measurement systems and in the single scale ratios without any calculation.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings in greater detail, and particularly FIGS. 1 and 2, the main body portion or guide rule 1 is provided with a generally spiral-shaped guide groove 3, throughout its length, and the. guide rule 1 itself is preferably of the same curving or generally spiral shape. The guide rule 1 is preferably constructed of substantially rigid transparent material with interchangeable graduation members 2, bearing scale graduation indicia, connected on one surface thereof. In the form of the invention shown in FIG. 2, the graduation members are on the lower surface of the transparent rule and the rule is trapezoidal in transverse section. This shape, with the downwardly diverging upper rule surfaces, is preferable because it provides better optical viewing of the scale graduation-s 2 through the transparent rule.

A flexible body assembly 4, which consists of a plurality of longitudinally extending resilient lamellas 5 connected together, is operatively connected for movement along guide groove 3 by guide rail 6. Guide groove 3, as shown in FIG. 1, is actually formed of two generally spiral shaped portions curving in opposite directions, each having an extremity which has an infinite radius of curvature, and with the said extremities arranged in longitudinal abutment, such as at the point in FIG. 1 designated Roo. The generally spiral shape of the guide groove 3 curve is defined by the tangent angle T of the curve according to the following approximation formula:

wherein in reference to FIG. 3; T is the angle between a line tangent to the curve at its origin and a line tangent to the curve at any given point on the curve and L is the distance along the curve from the origin to the given point.

In the preferred embodiment, the guide rule 1 is connected above the flexible body assembly as this construction provides the simplest construction or configuration for the flexible body assembly 4. The flexible body assembly is preferably transparent and is composed of a plurality of longitudinally extending single lamellas constructed of a transparent elastic or resilient material. such as a flexible plastic material. The plurality of lamellas 5 each have a length of approximately 16 to inches, are pellucid at least in the areas of the flexible assembly 4 through which it is desirable for the operator to see, and are movably connected to each other by suitable toothing, such as movable tongue and grooving joints, or by single clamps, not shown, as such connections are well known in the art. The flexible body assembly 4 is thus in effect an easily bendable flat tape having a width of approximately 2 inches and a length having a reasonable relation to the size of the spiral, such as of approximately 16 to 20 inches.

As shown in the upper portion of FIG. 1, the flexible body assembly 4 is sectioned longitudinally into substantially two symmetrical parts, and this sectioning becomes apparent for the first time as the assembly 4 is flexed into curvature by the spiral guide groove 3 as it is moved from the straight position indicated at A in the lower part of FIG. 1 to the curved position indicated at B in the upper part of FIG. 1. In the curved position at B, it will be noted that an odd number of lamellas are shown and half of the lamellas 5 lamella are immovably connected together at one end by any conventional means while the opposite ends fan out due to each lamella assuming a curvature of a different radius and sliding relative to the other lamella. The other half of the lamellas 5 and the same center lamella are immovably connected together at the opposite ends, while the ends of the said other half of the lamellas adjacent the immovably connected ends of the first group are free to fan out. Thus when there are an odd number of lamellas 5 as shown in the drawings the center lamella is common to each group, that is, the center lamella is connected at one of its ends with the end connection of one group and at its opposite end with the end connection of the other group. When an even number of lamellas are used there is no lamella that is common to each group.

The guide rail 6, which is constructed of a strip of resilient material, and has a portion extending into guide groove 3 forming a movable sliding connection therewith, is connected or plastic welded by means of depending portions at 6 to the flexible body assembly longitudinally thereof at least three points, namely at the opposite ends, at the mid-point of each of the immovably end connected lamella groups, and the symmetrical axial center of the assembly which is the assembly turning point. In the case where the flexible body assembly 4 is comprised of an odd number of lamellas, as shown in the drawings, the center connection 6 of the rail 6 to the axial center of the assembly is at the longitudinal center of the center lamella, as shown. When an even number of lamellas are used the centers of the two innermost lamellas are individually connected at 6' to rail 6 because this is the symmetrical axial center of the assembly. It could then be said that the flexible body assembly 4 is sectioned longitudinally and the guide rail 6 is connected along the section line.

The guide rail 6, as indicated, is constructed of a resilient material and as the assembly 4 is moved along the guide rule 1 and its guide groove 3, the rail 6 assumes different curvature, that is, it has the curvature of a turning line which matches the curvature of the groove 3 in the rule. As the guide rail 6 bends to conform to the curvature of the groove 3, it laterally flexes the flexible body assembly 4, through the connection point 6, to the desired circular arc. A clamping device of a type wellknown in the art per se is connected to one end of the lamellas of the flexible body to prevent undesirable longitudinal displacement of the lamellas 5 of the assembly 4.

The two outer edges of the flexible body assembly 4, that is the edges of the lamellas forming the lateral extremities of the assembly, which constitute the drawing edges, are provided with graduation indicia indicated at 8, such as graduations in mm. (millimeter) divisions or in inches, as indicated in FIG. 2. This allows a simple means of measuring all circular arc lengths.

A pointer or graduation reading line means 7 is connected to the guide rail 6 at the center point of the flexible body assembly, that is along the line IIII of FIG. 1. Pointer 7 moves with rail 6 and assembly 4 and aligns with the graduation indicia on scale 2 pertaining to the curvature of the longitudinal edges of flexible body assembly 4. By way of example, in FIG. 1, body 4 is illustrated in full lines in two different positions A and B along guide rule 1. In position A, pointer 7 is indicated as registering with scales 2 to indicate that the radius of curvature of both edges of body 4 is infinity, indicating that the edges of the body portion form straight edges in this position, that is:

In position B, pointer 7 indicates the edges of body 4 have a radius of curvature of and 200 mm., respectively, or

R: 150/200 mm.

Thus pointer 7 in cooperation with the scales 2 always gives an indication of the radii of curvature of the two edges of the body assembly 4.

The interchangeable scales 2 allow the curve member to be provided with different scale divisions according to the scale to be used. For instance, one scale can be placed in the rules which provides radii readings in millimeters, and another scale having radii indicia in inches may be interchanged by slipping the scales in and out of the curved body to allow the radii to be read in the measurement system with which the user wishes to work.

While the invention has been shown and described in certain preferred embodiments, it is realized that modifications can be made without departing from the spirit of the invention, and it is to be understood that no limitations upon the invention are intended other than those imposed by the scope of the appended claims.

I claim:

1. An adjustable French curve instrument for producing circular arcs of selected radii comprising, a guide rule, a substantially spiral guide groove in said guide rule, a body portion, guide means connected to said body portion and connected in sliding engagement in said guide groove, said body portion comprising a plurality of flexible lamella means movably guidingly connected to each other respectively and mutually shiftable relative to each other, and said guide means adapted to conform to the curvature of said guide groove as said body portion is moved longitudinally along said guide rule and flex said lamella means to arcs of selected radii.

2. An adjustable French curve as set forth in claim 1 in which said substantially spiral guide groove is of a form having a tangent angle T which is defined according to the following approximation formula:

where T is the angle between a line tangent to the curve at its origin and a line tangent to the curve at any given point on the curve, and L is the distance along the curve from the origin to the given point.

3. An adjustable French curve instrument as set forth in claim 1 including interchangeable graduation scale members selectively connectable on said guide rule, and said body portion and said graduation scale members removably connected to said guide rule.

4. An adjustable French curve instrument as set forth in claim 1 in which said outer lamella means of said body portion include measurement graduations along the lengths thereof.

5. An adjustable French curve instrument as set forth in claim 1 in which said body portion has a greater Width than said guide rule, and said guide rule is connected on top of said flexible body portion.

6. An adjustable French curve instrument as set forth in claim 1 in which the edges of said guide rule are of the same substantially spiral shape as said guide groove.

7. An adjustable French curve instrument as set forth in claim 1 including pointer means connected to said guide means and movable therewith, and said pointer means registerable with said graduation scale members to provide graduation information relative to the curvature of said lamella means.

References Cited UNITED STATES PATENTS 3,134,176 5/1964 Hoyle 33-177 2,155,169 4/1939 Moses 33-177 866,152 9/1907 Merritt 33-177 FOREIGN PATENTS 339,977 5/ 1936 Italy.

SAMUEL S. MATTHEWS, Primary Examiner 

